Catalyst for removal of sulphur oxides from flue gases of power plants

ABSTRACT

The present invention relates to the catalytic processes for rendering harmless the flue gases of the power stations or more precisely to the catalysts for sulfur oxides reduction to elemental sulfur. The novel catalyst presents the binary polycations of copper and zinc or copper and manganese incorporated into the low silica faujasite X (LSX) having transition metals ratio Cu:Zn or Cu:Mn in the range of 2:1 to 4:1.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Russia Application No.2019133972A filed Oct. 24, 2019, now Russia Patent No. 2729422, theentire disclosure of which is hereby incorporated by reference.

FIELD OF INVENTION

The present invention relates to the catalytic processes for renderingharmless the flue gases of the power stations or more precisely to thecatalysts for sulfur oxides reduction to elemental sulfur. The novelcatalyst presents the binary polycations of copper and zinc or copperand manganese incorporated into the low silica faujasite X (LSX) havingtransition metals ratio Cu:Zn or Cu:Mn in the range of 2:1 to 4:1. Thedistinctive feature of the catalyst preparation procedure consists ofthe cation exchange operation carrying out by partially hydrolyzed saltsof transition metals at the pH range of 5.2-5.8.

BACKGROUND ART

The present invention suggests the highly efficient catalyst for sulfurcompounds removal from the power station flue gases by means of theirreduction by carbon monoxide into elemental sulfur.

Coal firing power stations are responsible for 40% of the total nationelectric power output. The total content of sulfur compounds in thedomestic anthracite and bituminous coals makes up of 0.8-6.0% w. In theprocess of coal burning sulfur is converted into sulfur dioxide (SO₂)and sulfur trioxide (SO₃) which form sulfuric acid in the atmosphere.Finally, the latter falls on the ground in the shape of acid rains thatin turn are hazardous for population health and environment. In such amanner, rendering harmless the flue gases of power stations is thenation actual, serious problem.

Various catalytic processes are well known for the removal of thesesulfur compounds from the flue gases. For instance, U.S. Pat. No.4,963,520 discloses the process for SO₂ removal by means sulfur dioxideoxidation into sulfur anhydrate and production of the sulfuric acid. Themain features and merits of this process have been described in agreater detail in the Danish company Haldor Topsoe brochure:“SNOX™—Efficient and Economic removal of sulfur contaminated compoundsfrom flue gases.”, 1981. The main disadvantage of this process consistsof necessity collecting, storing and realization of significant volumeof low concentration sulfuric acid. Indeed, the power station havinginstalled capacity of 2,200 Megawatts has to burn ˜4 million Mt/yearfuel that in turn, even in the case of 0.5% w. sulfur content wouldcause approximately 200,000 Mt output of sulfuric acid of 33%concentration.

The catalysts, which allow the reduction of sulfur oxides into elementalsulfur are also well known and are characterized by more advantages. Thegeneral overview of those catalysts has been given in the paper D. C.Moody et al, “Catalytic Reduction of Sulfur Dioxide”, Journal ofCatalysis, v. 70 (1), 1981. It is also known U.S. Pat. No. 5,213,779that suggests to use metal lanthanides as the desulfurization catalystwhile U.S. Pat. No. 5,853,684 uses for the same purpose lanthanum oxidein combination with cobalt and strontium sulfides. The common demeritsof those catalysts include the high costs of the rare earth metals,their relatively low resistance to sulfation and high temperature(300-800° C.) requirement for their efficient application. The all thesefeatures lead to the significant rising the costs of the electric powerproduction.

Several other types of catalysts for intensive recovery of sulfur oxidesfrom flue gases have been formed which are based on the high silicazeolites USY, ZSM, SSZ-13 and so far. U.S. Pat. No. 6,974,787 employs asflue gas desulfurization catalyst vanadium-cerium exchanged forms of theultra-stable faujasite USY, whereas U.S. Pat. No. 7,572,414 usesvanadium, titanium, wolfram and molybdenum oxides which are loaded overhigh silica zeolite as a carrier. The high content of metals IY-VIgroups of the Periodic System in the catalysts composition and theirextremely high cost essentially limit possibility of commercialapplication of such catalysts.

It is also known the catalyst which is disclosed in U.S. Pat. No.7,960,307. According to the invention, the catalyst presents Zn-, Mn-,Cu- and Ni-exchanged forms of zeolites USY, BETA, ZSM, which arecharacterized by high ratio SiO₂:Al₂O₃ oxides, higher than 10.0, andinclude loaded over zeolite surface metal vanadate. The narrowcommercial availability of the high silica zeolites in the catalyst'scomposition, complexity of the process for catalysts preparation as wellas a low activity of the catalysts of the prior art in the reaction ofsulfur oxides reduction at the temperatures below 300° C. are the maindisadvantages of the known catalysts.

While these products have been useful for flue gases desulfurization, itis important to create the new catalysts which would overcome thedisadvantages of the prior art.

It is therefore an aspect of the invention to produce a novel catalystfor sulfur oxides reduction with improved efficacy in protection of theenvironment.

It is further aspect of the invention to produce Cu—Zn, Cu—Mn polycationexchanged forms of low-silica faujasite.

It is a still further aspect of the invention to produce a catalyst forflue gases desulfurization providing an activity in the low temperaturerange, below 240° C.

It is a still further aspect of the invention to provide a low-costcatalyst for use for flue gases desulfurization which does notessentially increase the cost of electric power output by the powerstations.

Still further objects and advantages will become apparent fromconsideration of the ensuing description of a preferred embodiment ofthe invention and the examples therewith.

SUMMARY OF INVENTION

In accordance with the present invention, there is provided a flue gasesdesulfurization catalyst, designed for the use at power stations, whichcatalyst comprises low-silica faujasite having silica to alumina oxidesratio on the level of 2.0-2.2 and contains the binary polycations oftransition metals: copper and zinc or copper and manganese at theirproportion Cu:Zn and Cu:Mn from 2:1 up to 4:1.

The invention is also a process for the production of this catalyst forsulfur oxides removal from flue gases.

The invention is also a process for flue gases desulfurization with useof the novel catalyst at the relatively low temperature range, below240° C.

DETAILED DESCRIPTION OF THE INVENTION

The catalyst product of this invention is a low-silica faujasite havinga molar ratio of silicon and aluminum oxides in the range of 2.0-2.2whereas the said low-silica faujasite contains the binary polycations oftransition metals copper and zinc or copper and manganese at theirproportion Cu:Zn or Cu:Mn from about 2:1 to about 4:1.

The procedure for low-silica faujasite synthesis has been described byG. Kul, (G. H. Kül, “Crystallization of Low-Silica Faujasite(SiO₂:Al₂O₃˜2.0”), Zeolites, 1987, 7, 451) and has been commercializedby several zeolite manufacturers. The simple process for zeolitespolycation forms synthesis has been developed by the authors of thepresent invention, which alongside the activity of zeolites with thetransition metals polycations in reactions of carbon monoxide andorganic sulfur oxides oxidation has been published in the followingpapers: O. P. Tkachenko, A. A. Greish, A. V. Kucherov, K. C. Weston, A.M. Tsybulevski, L. M. Kustov “Low-temperature CO oxidation by transitionmetal polycation exchanged low-silica faujasites”, Applied Catalysis B:Environmental, 2015, 179, 521 and A. M. Tsybulevski, O. P. Tkachenko, E.J. Rode, K. C. Weston, L. M. Kustov, E. M. Sulman, V. Y. Doluda, A. A.Greish “Reactive adsorption of sulfur compounds on transition metalpolycation-exchanged zeolites for desulfurization of hydrocarbonstreams”, Energy Technology, 2017, 5, 1627.

An enhanced activity of the catalysts of the present invention in theoxidation reactions is caused by the transition metal polycationsability for transferring excessive oxygen atoms of polycations to thereactants. At the same time, the activity of the polycation catalysts inthe reducing reactions, their capability to breaking away oxygen atomsfrom the reactants was unknown, was absolutely unexpected andsurprisingly found by the authors of the present invention. The activityof the novel catalyst at the low temperatures range, its capability forcomplete elimination of sulfur dioxide even at 240° C. is alsoabsolutely unexpected and amazing. The mentioned features of the novelcatalyst open new ways for the desulfurization of flue gases of powerstations.

In order to illustrate the present invention and the advantages thereoffor sulfur oxides removal from flue gases, the following examples areprovided. It is understood that these examples are illustrative and donot produce any limitation on the invention. In particular, it isimportant to understand that the present invention is generallyapplicable for power stations that are firing gas, liquid or solidfuels.

Examples 1-3 The Catalyst Samples Preparation

The preparation procedures, which are given below, are designated forobtaining ˜140 g of the final product. The all catalyst samples wereprepared on the basis of sodium-potassium form of zeolite LSX of the MChemical Co manufacturing

Example 1. Catalyst (Cu)_(p)(Zn)_(p)CaLSX-4

Although the cations of alkali and alkaline-earth metals play a balancedrole in the low-silica zeolite X structure, the preliminary conversionsodium-potassium form into calcium form is useful for the followingsynthesis of copper and zinc polycations. Thus, the preparationprocedure includes the following operations:

-   -   a) Exchange of the alkali cations for Ca²⁻⁺ cations.        -   Prepare 1 L of the 1N solution of calcium chloride by            dissolution of 73.5 g CaCl₂.2(H₂O) in deionized water (DIW);        -   Treat 100 g granule of the origin zeolite by 1 L of 1.0N            solution of CaCl₂ at the ambient temperature and proper            mixing. Maintain the pH of the exchanged solution in the            range of 6.5-7.0 to obtain ˜55-60%-exchanged CaLSX sample;        -   Wash the granules in ˜10 L of DIW.    -   b) Cu²⁺-exchange.        -   Prepare the buffer solution—0.05M basic sodium dihydro            phosphate by dissolution of 6 g anhydrous NaH2PO₄ in 1 L            DIW;        -   Prepare 1 L of 1N CuCl₂ solution by dissolution of 85.6 g            CuCl₂.H₂O in 1 L DIW and lower pH of the exchange solution            by addition of 35 ml of buffer to avoid a spontoon hydroxide            precipitation;        -   Treat the washed granules of CaLSX by 1 L of 1N solution of            CuCl₂ at ambient temperature and instant agitation over 4            hours. Maintain pH of the exchange solution on the level of            5.0-5.4 with the use of sodium-dihydrophosphate buffer. The            achieved ion exchange degree should be about ˜50% Cu, 40%            Ca;        -   Wash the exchange product by 10 L DIW.    -   B) Zn²⁺-exchange        -   Prepare buffer solution—0.03M basic potassium hydro            phosphate (K₂HPO₄). Dissolve 5.25 g K₂HPO₄ in 1 L DIW.        -   Prepare 1 L of 1.5N zinc chloride solution. Dissolve 102 g            anhydrous ZnCl₂ in 1 L DIW and to avoid the intense            precipitation of zinc hydroxide, lower the solution pH by            addition of 60 mL buffer.        -   Treat CuCaLSF, as it was obtained in the operation b) of the            catalyst sample (Cu)_(p)(Zn)_(p)CaLSX-4 synthesis by 1 L of            1.5N ZnCl₂ solution for 4 hours maintaining pH of the            exchange solution on the level of 5.6-6.0 by buffer—0.03M            K₂HPO₄.solution. The final cation ion exchange degrees in            the catalyst sample are: Ca—15%, Cu—50%, Zn—12.5%            equivalent.        -   Wash the product by DIW up to the negative reaction for            chloride ion by 0.028N AgNO₃ solution.

Example 2. Catalyst (Cu)_(p)(Zn)_(p)CaLSX-2

-   -   Replicate operations a) and b) of the above described procedure        for (Cu)_(p)(Zn)_(p)LSX-4 the catalyst synthesis.    -   c) Zn²⁺-exchange    -   Prepare 1 L of 2.5N zinc chloride solution. Dissolve 170 g        anhydrous ZnCl₂ in 1 L DIW and lower pH solution by 75 mL buffer        addition to avoid zinc hydroxide precipitation applying for the        purpose 0.03M K₂HPO₄ solution;    -   Treat the product of stage b) of the previous sample preparation        procedure, CuCaLSF sample by 1 L of 2.5N zinc chloride solution        over 4 hours maintaining pH of the exchange solution on the        level of 5.2-5.6 applying the K₂HPO₄ buffer solution. The        achieved ion exchange degrees in the final product are: Ca—12%,        Cu—45%, Zn—22% 3 KB.

Example 3. Catalyst (Cu)_(p)(Mn)_(p)LSX-2

-   -   Replicate a) and b) steps of the above described procedure for        the catalyst (Cu)_(p)(Zn)_(p)LSX-4 synthesis.    -   B) Mn²⁺-exchange    -   Prepare 1 L of 2N manganese chloride solution. Use 198 g        MnCl₂.4H₂O and dissolve it in 1 L DIW with the addition of 100        mL of buffer-potassium hydro phosphate to avoid manganese        hydroxide precipitation.    -   Treat the (Cu)_(p)CaLSF sample, which was obtained on the        step b) of the catalyst preparation over 4 hours by 1 L of 2N        manganese chloride solution maintaining pH of the exchange        solution on the level of 5.1-5.4 by means of K₂HPO₄ buffer. The        cation composition in the obtained product is: Ca—15%, Cu—50%,        Mn—25% equiv.

Example 4 Catalyst (Cu)_(p)(Zn)_(p)CaLSX-2 EXAFS Specters—Confirmationof the Catalyst Polycation Structure

EXAFS-specters of the catalyst (Cu)_(p)(Zn)_(p)CaLSX-2 sample wererecorded at the BM23 European Synchrotron Radiation Station (ESRF,Grenoble, France). The specters of metal foil were recordedsimultaneously for comparison. The measured parameters of copper andzinc cations are presented in Table 1.

TABLE 1 Polycations Cu and Zn Structure Parameters in the Catalyst(Cu)_(p)(Zn)_(p)CaLSX-2 Cation Me—O bond Surface Area length, Oxygen σ ×10⁻³, Cation Å Content, N Å⁻² Cu—O 1.97 ± 0.01 3.08 ± 0.19 4.7 ± 0.1Zn—O 2.05 ± 0.01 3.75 ± 0.16 9.4 ± 1  The results of spectralmeasurements unambiguously confirm copper and zinc polycations presencein the (Cu)_(p)(Zn)_(p)CaLSX-2 catalyst. The length of cation measuredradii significantly exceeds the standard bond length in monocations(1.97; 2.05 versus 1.95), while an average oxygen content is essentiallyhigher than stoichiometric one and the surface that is occupied by Cuand Zn polycations is 2-3 pa

a larger than monocation size.

Example 5 The Catalyst Activity Test

The catalyst samples of Examples 1-3 were tested for activity in thereaction of sulfur dioxide reduction by carbon monoxide alongside theLa₂O₃.TiO₂ (anatase) catalyst sample, which is known from U.S. Pat. No.5,213,779. The activity measurements were conducted with use of metalreactor of 9 mm diameter and 40 cm length. The sample granulation sizewas 1.6-2.0 MM. Preliminary samples training was carried out at 250° C.over 2 hours in nitrogen flow. The composition of initial gas mixturewas: SO₂—0.5%, CO—1.5%, He—98%. The gas volume rate—120-160 cm³/min. Thereaction temperature was varied in the 220-380° C. range.

The reaction products analysis was conducted by GC with the katharometerdetector with the use of three packed columns: Column 1—length 1.5M,stationary phase—molecular sieve 5 A; Column 2—length 1.5M, stationaryphase—Parapack Q; Column 3—length 2M, stationary phase—Chromosorb SE-54.

The test results are disclosed in Table 2.

TABLE 2 SO₂ Conversion Degree over Various Catalysts Depending on theReaction Temperature Conversion Degree, % mole Temperature, ° C.Catalyst 220 240 280 300 380 (Cu)_(p)(Zn)_(p)CaLSX-2. 92 100 100 n/d n/d(Cu)_(p)(Zn)_(p)CaLSX-4. 90 95 100 n/d n/d (Cu)_(p)(Mn)_(p)LSX-2 95 100100 H/ 

H/ 

La₂O₃•TiO₂ 0 0 15 42 98

The catalysts, according to the present invention demonstratedoutstanding efficiency in sulfur dioxide elimination and therefore inthe environment protection performance. As it can be seen from Table 2,the catalysts of the present invention are able to provide a practicallycomplete sulfur dioxide removal at the temperature that is 150° C. lowerthan the highest ability of the catalysts of prior art. Thus, it isapparent that the catalysts of the present invention can providesubstantial technical and economic achievements at their implementationat the power stations.

While the above description contains many specifics, these should not beconsidered as limitations on the scope of the invention, but rather anexemplification of one preferred embodiment thereof. Many othervariations of the catalyst composition are possible.

We claim:
 1. A catalyst for sulfur oxides removal from flue gases ofpower stations, comprising a low-silica faujasite LSX with the binarypolycations of transition metals of IB, IIB, VIIB and VIIIB groups ofthe Periodic System, wherein the low-silica faujasite is characterizedthe ratio of SiO₂:Al₂O₃ oxides from about 1.8 to about 2.2 and includesbinary polycations of copper and zinc at their correlation from about2:1 to about 4:1.
 2. The catalyst of claim 1, wherein the saidlow-silica faujasite includes the binary polycations of copper andmanganese at their correlation from about 2:1 to about 4:1.
 3. Thecatalyst of claim 1, wherein the said low-silica faujasite includes thebinary polycations of copper and manganese at their correlation fromabout 2:1 to about 4:1.